NOAA Interpolated Outgoing Longwave Radiation (OLR)

We are now updating the data periodically. If you have acquired the files after Apr 8th 2019, please redownload them. The data for 2018 was duplicated at the end of the daily file starting after Dec 31 2018 and values for 2017 were incorrect.

Outgoing Longwave Radiation (OLR) data from NCAR archives, with gaps then filled with temporal and spatial interpolation. For details of the interpolation technique
see Note by Liebmann and Smith (Bulletin of the American Meteorological
Society, June 1996).

Example FORTRAN code that will read the data from the netCDF file can be
found in
readolr.f

The header has 7 values stored as short integer in variable "info": julian day, lowest day value, lowest night value,
highest day value, highest night value,
original number missing on day grid, original number missing on night grid.

However, taking a daily mean of the day and night passes, as is done for this dataset, avoids the issue of which is observed first, and serves to reduce the effective time jump that occurs at the aforementioned longitude to 12 hours.

Satellites and Equatorial Crossing Times:

The following is a list of satellites used, with their initial equatorial
crossing times. Whenever available, we have used the 1430 crossing times.
After Mar 1 2001, we switched to NOAA16 which uses a 1350 crossing time
(NOAA14 had started to suffer from severe drift).
These correspond to the 'odd' numbered satellites (except for NOAA14, which
was an emergency replacement for the exploded NOAA 13). The 1430 crossing
times are preferred because they have been available for the longest time
(John Janowiak, personal communication). Note that each of the
satellites drifted considerably from its initial crossing time (see Bates
et al. 1996, Journal of Climate, page 429.). Anyone discovering huge heretofore undocumented variability
is advised to check the following table before publishing their result, as changing crossing times
can cause spurious variability, especially over land.
The difference between NOAA 14 and NOAA 12 for February, 1995 is
shown here.

As of March 12 1999, original pixel data was put into a 1x1 grid at NOAA's Climate Prediction Center (CPC). They
then interpolated this to a 2.5x2.5 grid which is what we use. Because of the change, there
are more interpolated grids than there were previously.

Due to satellite drift, NOAA 14 data starting 1 March 2001 have been
replaced with NOAA 16 data, so it is advisable to re-acquire data
beginning 1 January 2001.

We now retrieve data directly from NESDIS, rather
than getting it through NCAR. NCAR has
replaced missing days with another satellite with a different crossing time
(see table above). We now interpolate gaps without replacement.

If you use the Interpolated OLR data in a publication, please cite Liebmann and Smith (Bulletin of the American Meteorological
Society, 77, 1275-1277, June 1996).

Please note: If you acquire Interpolated OLR
data products from PSD, we ask that you acknowledge us in your use of the
data. This may be done by including text such as
Interpolated OLR data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA, from their Web site at
https://www.esrl.noaa.gov/psd/ in any documents or publications using
these data. We would also appreciate receiving a copy of the relevant
publications. This will help PSD to justify keeping the
Interpolated OLR data set freely available online in the
future. Thank you!